linux-kernel - Re: [PATCH RFC 2/2] kvm: set affinity hint for assigned device msi

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Date:	Mon, 17 Oct 2011 09:09:46 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] kvm: set affinity hint for assigned device msi

On Sun, Oct 16, 2011 at 03:12:23PM +0200, Michael S. Tsirkin wrote:
> On Thu, Oct 13, 2011 at 11:54:50AM -0300, Marcelo Tosatti wrote:
> > On Tue, Oct 11, 2011 at 08:38:28PM +0200, Michael S. Tsirkin wrote:
> > > To forward an interrupt to a vcpu that runs on
> > > a host cpu different from the current one,
> > > we need an ipi which likely will cost us as much
> > > as delivering the interrupt directly to that cpu would.
> > > 
> > > Set irq affinity hint to point there, irq balancer
> > > can then take this into accound and balance
> > > interrupts accordingly.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > > ---
> > >  virt/kvm/assigned-dev.c |    8 +++++---
> > >  virt/kvm/irq_comm.c     |   17 ++++++++++++++++-
> > >  2 files changed, 21 insertions(+), 4 deletions(-)

Or maybe even automatic in-kernel irq affinity disabled by 
default (to avoid interference with userspace pinning). 
All of that if it makes sense performance wise, of course.

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